The liquid crystal display device generates an image by making use of the optical anisotropy and polarization characteristics of the liquid crystal molecules. Because of the superiority and higher contrast in displaying the movement image, the liquid crystal display device has widely been applied to such electronic devices as televisions, displays, mobile phones, and panel computers.
Because the liquid crystal panel does not emit light, an additional light source is needed. FIG. 1 is a sectional schematic view of an existing liquid crystal display device, which includes a shell assembly, a liquid crystal panel 4, a backlight unit and so on. The shell assembly may include a front shell 1, a rear shell 2, a frame support 3 and so on that are combined to form the installation space. The liquid crystal panel 4 is installed between the front shell 1 and the frame support 3, and the front shell 1, in the shape of a frame, forms a display window 5 to allow the liquid crystal panel 4 to display outward; the backlight unit is installed between the rear shell 2 and the frame support 3 for providing a backlight light source for the liquid crystal panel 4.
As shown in the drawing, the backlight unit includes a light guide plate 6, a reflecting plate 7, a substrate 8 arranged at the side of the light guide plate 6, some light sources 9 installed on the substrate 8, and so on. At present, mostly an LED is used as the light source 9, and correspondingly the substrate 8 is an LED printed circuit board. The substrate 8 is in touch with the rear shell 2, thus transferring the heat generated by the LED to the rear shell 2 for dissipating the heat.
For better dissipating the heat generated by the light source 9, the substrate 8 is further provided at its rear side with a cooling plate. With the cooling plate in touch with the rear shell 2, the heat generated by the light source 9 is quickly transmitted to the rear shell 2 through the cooling plate to be dissipated.
Most of the existing liquid crystal display devices use the above-mentioned backlight unit, where the light source 9 emits light, which enters the light guide plate 6 and, by the guidance of the light guide plate 6, is projected onto the liquid crystal panel 4 through the light-outgoing top surface of the light guide plate 6. Besides, the light is better concentrated to the light-outgoing top surface by making use of the reflecting plate 7 below the light guide plate 6, thus the brightness being increased. However, because there is a certain distance between the light source 9 and the light guide plate 6, the light emitted from the light source 9 may escape from the top or bottom, etc., and cannot enter the light guide plate 6 completely, making the utilization ratio and transmittance of the light source 9 low.